Drought-tolerant Maize Research Articles

Drought patterns: their spatiotemporal variability and impacts on maize production in Limpopo province, South Africa

Due to global climate change, droughts are likely to become more frequent and more severe in many regions such as in South Africa. In Limpopo, observed high climate variability and projected future climate change will likely increase future maize production risks. This paper evaluates drought patterns in Limpopo at two representative sites. We studied how drought patterns are projected to change under future climatic conditions as an important step in identifying adaptation measures (e.g., breeding maize ideotypes resilient to future conditions). Thirty-year time horizons were analyzed, considering three emission scenarios and five global climate models. We applied the WOFOST crop model to simulate maize crop growth and yield formation over South Africa’s summer season. We considered three different crop emergence dates. Drought indices indicated that mainly in the scenario SSP5-8.5 (2051–2080), Univen and Syferkuil will experience worsened drought conditions (DC) in the future. Maize yield tends to decline and future changes in the emergence date seem to impact yield significantly. A possible alternative is to delay sowing date to November or December to reduce the potential yield losses. The grain filling period tends to decrease in the future, and a decrease in the duration of the growth cycle is very likely. Combinations of changed sowing time with more drought tolerant maize cultivars having a longer post-anthesis phase will likely reduce the potential negative impact of climate change on maize.

Relationships between Grain Weight and Other Yield Component Traits of Maize Varieties Exposed to Heat-Stress and Combined Heat- and Water-Stress Conditions

It is necessary to identify the appropriate traits that influence yield in a given environment as part of a breeding programme. The objective of this study was to identify the morphological traits that contribute to maize grain weight (GWt) under abiotic stress conditions. Three drought-tolerant maize varieties were grown under no-stress (NHWS), heat-stress (HS), and combined heat- and water-stress (CHWS) conditions. Data from 19 morphological traits were analysed. The correlation results revealed that eight traits consistently produced a significant positive relationship with GWt under the three growth conditions. The path coefficient analysis revealed that in the NHWS, HS, and CHWS conditions, five traits consistently had a positive direct effect on the GWt. Given the magnitude of the positive direct effects, increasing dry biomass yield, harvest index, and grain number in the NHWS; grain number, harvest index, and ear width in the HS; and harvest index, days till silk appearance, leaf chlorophyll content, and grain number in the CHWS will increase GWt. Under various abiotic stress conditions, maize phenotypic expression varied. Therefore, the identified traits that contributed positively to GWt under various stress conditions should be considered when developing a maize improvement programme in a stress-prone environment.

Drought tolerant maize hybrids have higher yields and lower water use under drought conditions at a regional scale

Drought is an enduring abiotic constraint to stable and consistent maize productivity under climate change, especially for low rainfall regions with limited irrigation. One adaptation for severe drought is using drought-tolerant (DT) hybrids. Here, we characterize differences between conventional and DT hybrids in terms of yield and water-use efficiency under drought conditions at a regional scale of the Texas High Plains (THP). Using a validated version of APSIM-Maize, we simulated yields of conventional and DT hybrids across 11 water regimes and 25 counties in THP from 1984 to 2018. When irrigation amounts were constrained to 90%, 80%, 70%, 60% and 50% of total irrigation used for the baseline scenario (BS; a simulated scenario of conventional hybrid under full irrigation), DT hybrids showed lower yield penalties under drought stress relative to conventional hybrids. This improved total production by 19%, 24%, 26%, 26%, and 21% for each of the above irrigation levels. When the yield-target was set as 90%, 80%, 70%, and 60% of BS, total regional irrigation applied to DT hybrid could be saved more than that to the conventional hybrid, and therefore reduced more 17%, 16%, 15%, and 15% of BS irrigation, respectively. We showed that DT hybrids had greater yield gain and water savings through improved water productivity under deficit irrigation, highlighting the potential of deficit irrigation for increasing yield for the adoption of DT hybrid. Our quantitative evaluation of the yield advantage and water saving potential associated with DT hybrids also highlighted the regional benefits associated with adoption of drought adaptive hybrids.

Sustained improvement in tolerance to water deficit accompanies maize yield increase in temperate environments

AbstractStudies at a regional scale suggest that although maize (Zea mays L.) yield increased substantially, sensitivity to water deficit also increased concurrently with crop improvement. This study assessed changes in yield and yield stability after two decades of breeding by evaluating two cohorts of hybrids released by the AQUAmax program and comparing them to a non‐AQUAmax control. Studies were conducted in 2019 and 2020 seasons at four sites under well‐watered, moderate and severe stress conditions. Plant densities varied from 2.5 to 12.5 pl m−2. AQUAmax hybrids yielded more than non‐AQUAmax hybrids under water deficit conditions with the magnitude of the difference dependent on plant density. The sensitivity in yield across environments with a wide range of total crop evapotranspiration (350–800 mm) was lower for AQUAmax than non‐AQUAmax, so both yield and yield under stress conditions (yield stability), were enhanced for AQUAmax hybrids. The median differences between observed yields and the 80% quantile yield–evapotranspiration front were 379 for AQUAmax and 427 g m−2 for non‐AQUAmax hybrids. We conclude that deliberate selection of hybrids for yield performance under water deficit underpinned the sustained improvement in yield stability after two decades of drought breeding. Future research should focus on understanding the root causes for the suboptimal utilization of drought tolerant maize for the diversity of environments at a regional scale.

Effects of Phloem-Feeding Pest, Dalbulus maidis on Morphological Expression of Drought-Tolerant Traits in Maize

Drought is amongst the most important stressors affecting maize production globally. Existing strategies to offset drought impacts are centered around the rapid development of drought-tolerant cultivars through plant breeding. However, under both current conditions and projected climate changes, additional stressors such as insect pests will co-occur. To determine the impact of combined insect and drought stress on drought tolerance in maize, we assessed the effects of Dalbulus maidis, drought, and both stresses combined in drought-tolerant maize hybrids. We measured several maize morphological growth traits (i.e., plant height, stem diameter, shoot weight, root weight, root length, and root-to-shoot ratio) at the end of a 28-day period of pulse-stress and no-stress control exposure. We found that seedling growth declined when both stressors co-occurred. Nevertheless, drought-tolerant maize hybrids remained strongly tolerant to drought regardless of D. maidis infestation. While our results showed that drought tolerance is maintained in drought-tolerant maize seedlings, future studies should address any effects on maize yield. Our study highlights the importance of testing the combined effects of drought and insect stressors to better predict insect–plant interactions in the context of plant breeding for drought-tolerant traits in a changing climate.

English

Stay green is the plant’s ability to sustain photosynthetically functional green leaf area for longer periods, even with excessive water stress. This study was done to understand the gene action that controlled inheritance of the stay green trait with the general objective of contributing to breeding more drought tolerant maize varieties. 10 F1 hybrids from crosses between highly performing and the least performing drought tolerant inbred lines as regards selected stay green physiological determinants were planted under a rain out shelter with a well-watered control and excessive water-stress treatments applied from six weeks after planting and eight weeks after planting. With progress in days after flowering, data were collected on relative chlorophyll per unit leaf area (RC: LAUG), maximum quantum yield of photosystem II photochemistry (ΦII), non-photochemical quenching (NPQ) and linear electron flow (LEF). RC: LAUG and NPQ were mainly inherited by additive gene action. ΦII was controlled more by the environment than interallelic interactions while LEF inheritance was controlled mainly by interallelic interactions. Key words: Additive, inheritance, non-additive, photosynthesis, stay green.

Transcriptomic and physiological responses of contrasting maize genotypes to drought stress.

Drought is a significant environmental stress factor that adversely affects maize productivity. However, many details regarding the molecular mechanisms of maize against drought are still unclear. In this study, leaf transcriptomics and physiological traits of two maize genotypes with differing drought resistance were analyzed. Transcriptome sequencing identified 8985 and 7305 differentially expressed genes (DEGs) in SD902 and SD609, respectively. Functional analysis suggested that numerous genes are highly involved in oxidative defense, protein modification, photosynthesis, phytohormone response, MAPK signaling, and transcription factors (TFs). Compared to SD902, SD609 had a higher expression of DEGs related to antioxidant enzymes, photosynthetic electron transport, heat shock proteins, and indole-3-acetic acid (IAA) signaling under drought conditions, which might contribute to its tolerance mechanisms to drought. Stress-induced TFs may play a crucial regulatory role in genotypic differences. Moreover, the physiological changes and gene expression abundance determined using quantitative reverse transcription polymerase chain reaction were consistent with the RNA sequencing data. The study results suggest that the higher drought tolerance of SD609 than SD902 can be attributed to stronger stress defense capabilities, IAA signal transduction, and more stable photosynthesis. Our findings provide new insights into the molecular mechanisms of maize against drought stress, and the candidate genes identified may be used in breeding drought-tolerant maize cultivars.

Changes in Climate Extremes and Their Effect on Maize (Zea mays L.) Suitability Over Southern Africa

Southern Africa has been identified as one of the hotspot areas of climate extremes increasing, at the same time many communities in the region are dependent on rain-fed agriculture, which is vulnerable to these rainfall and temperature extremes. The aim of this study is to understand changes in extreme indices during the agricultural season under climate change and how that affect the modeling of maize suitability in Southern Africa. We analyze the changes in rainfall and its extreme indices (consecutive dry days, heavy rain events and prolonged rainfall events), and temperature and its extreme indices (hot night temperatures, hot day temperatures and frequency of very hot days) from the past (1986–2014) to the future (2036–2064) and integrate these into a maize suitability model. Temperature extremes are projected to increase in both duration and intensity, particularly in the eastern parts of the region. Also, consecutive dry days are projected to increase over larger areas during the agricultural season, while rainfall will be less in sums, heavier in intensity and less prolonged in duration. Including extreme climate indices in maize suitability modeling improves the efficiency of the maize suitability model and shows more severe changes in maize suitability over Southern Africa than using season-long climatic variables. We conclude that changes in climate extremes will increase and complicate the livelihood-climate nexus in Southern Africa in the future, and therefore, a set of comprehensive adaptation options for the agricultural sector are needed. These include the use of heat, drought and high-intensity rainfall tolerant maize varieties, irrigation and/or soil water conservation techniques, and in some cases switching from maize to other crops.

Peningkatan Produktivitas Jagung pada Lahan dengan Cekaman Naungan dan Kekeringan Melalui Penerapan Teknologi Adaptif dan Efisien

<p>Abiotic stress in the form of shading and drought in maize cultivation on rainfed land among plantation crops reduces yield. Therefore, an efficient and adaptive technology package is needed in this growing environment. This study aims to: 1) determine the technical and financial feasibility of the technology package for shade and drought tolerant maize cultivation on rainfed dry land between plantation crops (coconut), and 2) obtain recommendations for shade and drought tolerant varieties. The study was conducted through three trials in two locations in Gorontalo Regency, Gorontalo Province, in 2019 and 2020. To determine the technical feasibility, a field experiment was carried out using a randomized block design method with the introduction of technology package for shade and drought tolerant maize cultivation as a treatment, using 12 hybrid and composite maize varieties. Experiment I had five treatments with six replications, experiment II had eight treatments with four replications, and experiment III consisted of nine treatments with three replications. To determine the financial feasibility, used the partial budget analysis method. The results showed that the technology package for introducing shade and drought tolerant maize cultivation technology was technically and financially feasible, so it was recommended to replace the existing technology. The introduced technology package could increased maize productivity by 72% from an average of 1.706,43 kg/ha to 2.939,45 kg/ha, compared to the existing technology. The change in the use of existing technology to the introduction of maize cultivation technology gave a rate of return (R) = 1,89. In addition, the value of the R/C ratio, B/C ratio, and MBCR were greater than 1. The income from the application of introduced technology was an average of Rp 5.256.815/ha, higher than the existing technology of Rp 2.029.720/ha. The maize varieties recommended for their adaptability and efficiency in areas under both shade stress and drought with a combination of application of the introduction technology package were JH27, HJ21, Nasa-29, NK Sumo, Bisi-18, and Sinhas.</p>

ITRAQ-based quantitative proteomic analysis provides insight into the drought-stress response in maize seedlings

Drought is a major abiotic stress that harms plant cell physiology and limits the growth and productivity of crops. Maize (Zea mays L.), one of the most drought-susceptible crops, is a major food source for humans and an important resource for industrial bioenergy production; therefore, understanding the mechanisms of the drought response is essential for maize improvement. Using isotopic tagging relative quantitation (iTRAQ)-based protein labeling technology, we detected the proteomic changes in maize leaves under drought stress. Among the 3063 proteins that were identified, the abundance of 214 and 148 proteins increased and decreased, respectively, after three days of drought treatment. These differentially abundant proteins (DAPs) were mainly involved in cell redox homeostasis, cell wall organization, photosynthesis, abscisic acid biosynthesis, and stress-response processes. Furthermore, some of the DAP abundances still differed from the control six days after the drought treatment, most of which were molecular chaperones, heat shock proteins, metabolism-related enzymes, hydrolases, and transmembrane signal receptors. The expression level of some DAPs returned to normal when the water supply was restored, but for others it did not. A significant correlation between the protein and transcript levels was observed following an RT-qPCR analysis. Finally, our research provides insights into the overall mechanism of drought-stress tolerance, and important information for breeding of drought-tolerant maize.

Recent Advances for Drought Stress Tolerance in Maize (Zea mays L.): Present Status and Future Prospects.

Drought stress has severely hampered maize production, affecting the livelihood and economics of millions of people worldwide. In the future, as a result of climate change, unpredictable weather events will become more frequent hence the implementation of adaptive strategies will be inevitable. Through utilizing different genetic and breeding approaches, efforts are in progress to develop the drought tolerance in maize. The recent approaches of genomics-assisted breeding, transcriptomics, proteomics, transgenics, and genome editing have fast-tracked enhancement for drought stress tolerance under laboratory and field conditions. Drought stress tolerance in maize could be considerably improved by combining omics technologies with novel breeding methods and high-throughput phenotyping (HTP). This review focuses on maize responses against drought, as well as novel breeding and system biology approaches applied to better understand drought tolerance mechanisms and the development of drought-tolerant maize cultivars. Researchers must disentangle the molecular and physiological bases of drought tolerance features in order to increase maize yield. Therefore, the integrated investments in field-based HTP, system biology, and sophisticated breeding methodologies are expected to help increase and stabilize maize production in the face of climate change.

Effect of Nitrogen Fertilizer and Soil Moisture Levels on the Performance of Drought-Tolerant Maize on Ferric Luvisol and Rhodic Ferralsol Soils

Globally, water and nitrogen have been known as the most important resources that significantly impact crop productivity. This study assessed the response of Water Efficient Maize for Africa, WEMA3127 variety to different soil moisture levels, and nitrogen fertilizer rates on Ferric Luvisol and Rhodic Ferralsol soils. A greenhouse experiment was conducted to investigate the effect of different N fertilizer and soil moisture levels on the growth, yields and water-use efficiency of the water-efficient maize for Africa (WEMA) variety on two distinct soils. The experiment was designed as a completely randomized design with three replicates and used a factorial design with a 5 x 2 x 2 design. Treatments comprised five N fertilizer rates (0, 60, 120, 180 and 240 kg N/ha), two soil moisture levels (45 and 100% field capacity), and two soil types (Ferric Luvisol and Rhodic Ferralsol). Plant height, chlorophyll content and total dry matter weight as growth attributes, grain yield, total biological yield and water-use efficiency parameters were determined. The tallest plant height (283.33 cm) was recorded in Ferric Luvisol supplied with 240 kg N/ha at 100% field capacity. The highest grain yield (136.8 g /pot) and water-use efficiency (1.94%) were obtained in Rhodic Ferralsol treated with 180 kg N/ha at 100% and 45% field capacity (FC), respectively. A linear relationship was obtained between N fertilizer rates and the grain yield (R2 = 0.91) and between total dry matter and grain yield (R2 = 0.51). The results showed that the growth and water-use efficiency of WE3127 maize variety was better on Rhodic Ferralsol than in Ferric Luvisol.

Integrating GWAS and TWAS to elucidate the genetic architecture of maize leaf cuticular conductance.

The cuticle, a hydrophobic layer of cutin and waxes synthesized by plant epidermal cells, is the major barrier to water loss when stomata are closed. Dissecting the genetic architecture of natural variation for maize (Zea mays L.) leaf cuticular conductance (gc) is important for identifying genes relevant to improving crop productivity in drought-prone environments. To this end, we performed an integrated genome- and transcriptome-wide association studies (GWAS and TWAS) to identify candidate genes putatively regulating variation in leaf gc. Of the 22 plausible candidate genes identified, 4 were predicted to be involved in cuticle precursor biosynthesis and export, 2 in cell wall modification, 9 in intracellular membrane trafficking, and 7 in the regulation of cuticle development. A gene encoding an INCREASED SALT TOLERANCE1-LIKE1 (ISTL1) protein putatively involved in intracellular protein and membrane trafficking was identified in GWAS and TWAS as the strongest candidate causal gene. A set of maize nested near-isogenic lines that harbor the ISTL1 genomic region from eight donor parents were evaluated for gc, confirming the association between gc and ISTL1 in a haplotype-based association analysis. The findings of this study provide insights into the role of regulatory variation in the development of the maize leaf cuticle and will ultimately assist breeders to develop drought-tolerant maize for target environments.

Combining Climate Smart Agriculture Practises Pays Off: Evidence on Food Security From Southern Highland Zone of Tanzania

Concerns of food insecurity and climate change are serious global challenges, Tanzania included. In response, farm households are using various climate-smart agricultural practises (CSA-practises) which are believed to play a vital role to increase agricultural productivity, increasing resilience to climate change, and reducing mitigation costs for greenhouse gas (GHG) emissions while improving households' food security. Despite these benefits of CSA-practises but the usage of these practises is still voluntary and its impact on household welfare specifically food security is not well-documented in Tanzania, particularly in Mbeya and Songwe Region. Therefore, the determinants of using CSA-practises (in particular organic manure, drought-tolerant maize seeds, and irrigation) and the impact of the usage of household food security was examined. The cross-sectional study design was used to collect information from farming households in the Southern Highlands of Tanzania (Mbeya and Songwe regions). To evaluate the impact of the combination of CSA-practises on household food security the study used a multinomial endogenous treatment effect model. A counterfactual analysis was conducted to compare the impacts from different combinations of CSA-practises considered. The findings show that household, plot, and institutional characteristics have significant effects on the usage of a different combination of CSA-practises. The study also found that the highest payoff of food security is achieved when CSA-practises are used in combination rather than in isolation. The package that contains a combination of drought-tolerant maize seeds and Irrigation (Or0Dt1Ir1) gave a higher payoff than the combination of all three CSA-practises. The study suggests that based on the practises considered in this study, the usage of a combination of various practises results in better food security compared to the usage of these practises individually. This indicates that promoting a combination of CSA-practises could enhance household food security.

Variation in Maize Grain Yield Indices When Exposed to Combined Heat and Water Stress Conditions under Different Soil Amendments

Increased yield can be achieved by optimising the growth environment, improving the plant gene pool, or a combination of the two. This study’s objective was to evaluate the effect of combined heat and water stress (CHWS) on maize yield, grown in various soil conditions. The experimental design was a four-replicated 3 × 3 × 2 × 3 factorial in a completely randomized design. Three water stress levels, three soil amendments, two soil textural types, and three drought-tolerant maize varieties were combined to create 54 treatment interactions. The result showed that as the severity of the water stress increased, the yield decreased. The near terminal water stress reduced cob weight, grain weight, and grain number by 96, 97, and 97%, respectively. The maize varieties were ranked WE5323 ≥ ZM1523 > WE3128 in terms of average performance and stability. Under heat and moderate water stress, the poultry manure amendment performed well for WE5323 and ZM1523, while the mineral fertilizer amendment performed best for WE3128. Compared to the inorganic amendment, the organic had a greater ameliorative capacity for grain yield under CHWS. For improved grain yield under CHWS, farmers are advised to grow WE5323 and ZM1523 with organic amendments. The findings in this study could improve food security strategies for low-income households living in high-stress environments.

Assessing the Fodder Potentials of Drought-Tolerant Maize (Zea mays L.) Hybrids in West Africa

The study evaluated the fodder potential of 42 promising drought-tolerant (DT) three-way cross maize (Zea mays L.) hybrids, 11 commercial hybrid checks, and 1 local variety check under irrigation. Agronomic and laboratory trials were conducted to determine their morphological traits and fodder potential. Hierarchical cluster analysis (HCA) to group cultivars into clusters is based on quantity, quality, and the combination of both variables. Selection of potential food-feed cultivars was based on the quantity traits (grain and biomass yield) and quality traits crude protein (CP), in vitro organic matter digestibility (IVOMD), and metabolizable energy (ME). Variation was found for dry matter yield (DMY) at harvest as commercial hybrid recording the maximum DMY of 14.1 t ha−1 and the highest grain yield of 1.4 t ha−1 (P < 0.01), while local check produced a minimum grain yield of 0.54 t ha−1 (P < 0.01) with grain moisture content range between 8.4 and 11.6%. The maximum mean ash content was 5.8% for DT hybrids. Average CP was the highest in commercial hybrids with a value of 6.1%. The mean values for ME were similar (P > 0.01) in both commercial hybrids (7.2 MJ/kg DM) and DT hybrid (7.2 MJ/kg DM), while the highest ME (7.6 MJ/kg DM) was recorded for the local check. Ranking of the hybrids based on grain yield, DMY, CP, ME, and IVOMD showed that cluster subgroup A3 (M1124–24, M1527-7, 30F32, and M1427-6) and A4 (M1427-3, SC637, and M1627-11) exhibited the best potential traits and can therefore be recommended for commercial cultivation following adoption trials by farmers.

Dissection of Maize Drought Tolerance at the Flowering Stage Using Genome-Wide Association Studies.

Drought is one of the most critical environmental factors constraining maize production. When it occurs at the flowering stage, serious yield losses are caused, and often, the damage is irretrievable. In this study, anthesis to silk interval (ASI), plant height (PH), and ear biomass at the silking date (EBM) of 279 inbred lines were studied under both water-stress (WS) and well-water (WW) field conditions, for three consecutive years. Averagely, ASI was extended by 25.96%, EBM was decreased by 17.54%, and the PH was reduced by 12.47% under drought stress. Genome-wide association studies were carried out using phenotypic values under WS, WW, and drought-tolerance index (WS-WW or WS/WW) and applying a mixed linear model that controls both population structure and relative kinship. In total, 71, 159, and 21 SNPs, located in 32, 59, and 12 genes, were significantly (P < 10−5) associated with ASI, EBM, and PH, respectively. Only a few overlapped candidate genes were found to be associated with the same drought-related traits under different environments, for example, ARABIDILLO 1, glycoprotein, Tic22-like, and zinc-finger family protein for ASI; 26S proteasome non-ATPase and pyridoxal phosphate transferase for EBM; 11-ß-hydroxysteroid dehydrogenase, uncharacterised, Leu-rich repeat protein kinase, and SF16 protein for PH. Furthermore, most candidate genes were revealed to be drought-responsive in an association panel. Meanwhile, the favourable alleles/key variations were identified with a haplotype analysis. These candidate genes and their key variations provide insight into the genetic basis of drought tolerance, especially for the female inflorescence, and will facilitate drought-tolerant maize breeding.

Dot Blot Assay for Assessing Trehalose-6-phosphate Synthase Gene Expression in a Maize Breeding Population under Water Stress

Field maize is an important economic crop grown around the world and it has been mainly used in the animal feed industry. Maize yields have been inadequate for the demand due to drought events. One way to alleviate yield losses is to develop drought tolerant maize varieties for farmers. Trehalose-6-phosphate synthase (TPS) is an important enzyme involved in trehalose biosynthesis which has been found to increase plant tolerance to abiotic stresses. The aim of this research was to screen the levels of TPS gene expression in maize breeding materials under water stress via dot-blot hybridization using cDNA probe. To do so, 34 S2 maize families were grown and subjected to water stress condition. Leave samples were collected at 6 different days after planting (DAP) for a dot blot assay. The results showed that the level of TPS gene expression was highest at 4 days after stress (relative intensity at 64 DAP). However, dot blotting at 6 days after stress (relative intensity at 66 DAP) was effective to differentiate maize families. Furthermore, a moderate negative relationship between relative signal intensity at 66 DAP (RI66) and Smith index based on multi-phenotypic traits was found to be statistically significant. Our study showed that maize with high TPS gene expression tended to be less tolerant to water stress. It is noteworthy that the study of TPS gene expression in mature maize under stress in this study showed results that contrasted with previous reports on seedlings in many plant species. Furthermore, we found that 4 out of 34 S2 maize families may have potential for further use in our breeding program.

Response of Maize-Hybrids Phenology Under high Plant Population Density in parts of Northern Guinea Savanna of Nigeria

Plant distribution in the field, as affected by plant density, has been one area that has received a great deal of attention over the last several decades. Population density, whether directly on the plant or indirectly on biotic factors associated with plant density is one of the most important factors in determining physiological attributes of a crop. Maize grain yield has a parabolic response to stand density that maximizes yield, which is widely known by the crop managers, physiologists and breeders; together with the concept that this optimum stand density varies with the environment. Development of breeding populations and hybrids with improved tolerance to high plant densities should be an important part of maize breeding programs. A field experiment was therefore conducted during 2015 and 2016 rainy season at Tudun Wada, Kano and Shika, Zaria in the Northern Guinea savanna of Nigeria in order to assess the phenological components of maize-hybrids at high plant population density. The experiment consisted of two plant populations of 53,333 plantha-1 and 88,888 plantsha-1 as main plot and eight recently developed drought–tolerant maize hybrids: M0826-7, M0926-8, M1026-10, M1026-13, M1124-4, M1124-10, M1227-12 and M1227-14 and two widely cultivated commercial hybrids as controls (Oba-98 and Oba super-1) as sub-plots laid out in a randomized split-plot design and replicated three times. Maize-hybrids responded to high plant population density in the two locations. Increasing plant population significantly decreased the phenology of maize-hybrids, which showed better adaptation of hybrids to high plant population density. Hybrids showed shorter days to maturity and shorter anthesis-silking interval. Maize-hybrids performed better at Zaria than at Tudun Wada because rainfall was higher and better distributed in this location. However recent hybrids were more tolerant to high plant population than the commercial hybrids, therefore the recently released maize-hybrids were more adapted to biotic stress.&#x0D; Keywords: Biotic stress, Growth, Phenology, Plant population density and Maize-hybrids

The Influence of Parental Heat-Stress Priming on Drought-Tolerant Maize Progenies’ Field Performance

Maize (Zea mays L.) is a staple crop and an industrial crop. Improving its thermotolerance will be a crucial step in ensuring food security. The objective of this research was to assess the influence of the parental growth environment on their progenies in a non-heat stress environment. The progenies evaluated in this field study were obtained from a 2 × 3 × 3 factorial in a completely randomised greenhouse experiment. Two contrasting growth environments, three maize varieties, and three soil amendments were used in the greenhouse study. A randomised complete block design experiment with three replications was used to grow the progenies. The progenies were examined for nineteen morphological attributes. In this study, 69.51% of the yield variation was explained by the first and second principal component axes. Among the studied attributes, grain weight and cob weight explained more variations in the progenies than the other attributes. The interaction of the parental heat-stress and soil amendment conditions elicited different responses from the drought-tolerant maize progenies. Based on the differences in their yield attributes, the progenies were grouped as poor yielders (Cluster IV), good yielders (Cluster I) and high yielders (Clusters II and III). The parental growth environment influenced the progenies’ field performance in a non-heat-stress environment. Further evaluation of the progenies under a heat-stress environment and molecular analyses are required to establish that a transgenerational effect has occurred.